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EQ8 PE curve

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#1 pereloup

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Posted 23 October 2013 - 11:17 AM

Hello,

I just recieved my Sky-Watcher EQ8 mount. I know some of you want to know how it compares to other mounts in this range.

Here is my setup:

EQ8 mount on its pier/tripod
Celestron EdgeHD 8"
Stellarvue SV80ST with TRF-2008 0.8x reducer
Lodestar autoguider camera on the Stellarvue SV80ST

Here is the PE curve from PecPrep v1.94. The data are extracted form the PHD Guiding logfile from the Lodestar camera attached on the Stellarvue SV80ST at 384 mm focal length.

Posted Image

Remember that I'm a first time user of PecPrep. The blue curve is the raw data from PHD Guiding. The red line is the smoothed PE and the green line is the noise after removing the smoothed curve from the raw data. If I read the stats correctly (and correct me if I'm wrong) the important numbers here are those in the red circle with a mean PE of +/-2,2 arcsec.

Here is a 10 min unguided sub at 384 mm focal length. You can see a small drift due to a not so perfect polar alignment:

Posted Image

Higher resolution here: 10 min unguided sub with EQ8

Stephan

________________________
Edit:

Following an advice below, I tried with a better resolution and found a PE of +/-2.8 arcsec.
Posted Image

#2 Wembley2000

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Posted 23 October 2013 - 12:05 PM

Very nice result, was the declination compensation entered in pecprep?

#3 pereloup

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Posted 23 October 2013 - 12:10 PM

Very nice result, was the declination compensation entered in pecprep?


Yes it was. The polar alignment was not spot on.

Stephan

#4 Wembley2000

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Posted 23 October 2013 - 12:22 PM

Ok, some people miss that when using pecprep. Great result. One recommendation I would have is to shoot at a higher focal length, pempro recommends less than 2 arc/sec per pixel.

Wem

#5 orlyandico

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Posted 23 October 2013 - 12:55 PM

it's actually the first two numbers that are the peak-to-peak PE, which in this case is +/- 4" or so. Since auto-filter has already been clicked. The +/- 2" is RMS PE, that's not what we want. Try to un-click all the harmonics except the fundamental (the highest one, with 200-second period). so we can see the fundamental worm PE. Strange though that the extra terms are all slower than the fundamental. Normally the extra terms are caused by the gearbox and are faster than the fundamental..

#6 famax

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Posted 23 October 2013 - 06:17 PM

No gear box in the eq8 ;)
nice results , should give good results once autoguided !!

#7 pereloup

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Posted 23 October 2013 - 09:04 PM

Ok, some people miss that when using pecprep. Great result. One recommendation I would have is to shoot at a higher focal length, pempro recommends less than 2 arc/sec per pixel.

I will try that on the EdgeHD soon and post results. Thanks.


it's actually the first two numbers that are the peak-to-peak PE, which in this case is +/- 4" or so. Since auto-filter has already been clicked. The +/- 2" is RMS PE, that's not what we want. Try to un-click all the harmonics except the fundamental (the highest one, with 200-second period). so we can see the fundamental worm PE. Strange though that the extra terms are all slower than the fundamental. Normally the extra terms are caused by the gearbox and are faster than the fundamental..

OK, I think I understand. Here is the results if I unclick all the harmonics.

Posted Image


No gear box in the eq8

It's partly true. The DEC is direct drive but there is a 1:1 belt between the motor and the worm gear in RA.


Stephan

#8 orlyandico

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Posted 23 October 2013 - 10:47 PM

ok so the worm fundamental is +4" / -4" which is good but not mind-boggling. Tak NJP's are usually under +2" / -2" (so are AP900s) but of course they cost a lot more.

Conclusion, it seems to have similar PE as the CGE Pro, with a similar price as the CGE Pro. But I think it carries more payload?

I'm curious though - so it uses a direct drive stepper motor with no gearbox? is it a friction drive like the Gemini G53f?


#9 famax

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Posted 24 October 2013 - 02:41 AM

No, as said by stephan the ra block is belt driven by a 1 :1
gear, so no classical noise induced by direct contact gear reduction ...
the dec motor is directly coupled to the worm.

#10 orlyandico

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Posted 24 October 2013 - 02:56 AM

Yup I found this page -

http://www.dangl.at/.../eq8/eq8_e4.htm

so it is a large stepper motor - looks like a NEMA23 - which is microstepped at 1/64 and with no reduction to the worm wheel. Interesting concept. Somebody has done this with a G11 and Littlefoot. More spendy motors, but no gearbox noise. Good approach! :)

Can you confirm the rumor that this EQ8 is actually a Hungarian design from Ursa Minor that was sold to Skywatcher?

#11 pereloup

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Posted 24 October 2013 - 05:03 AM

ok so the worm fundamental is +4" / -4" which is good but not mind-boggling. Tak NJP's are usually under +2" / -2" (so are AP900s) but of course they cost a lot more.

Here in Canada, the EQ8 is 3800$ including the pier/tripod. I was tempted by Astro-physics for a while, but at over 12000$ (if you include tripod, counterweight, shipping, customs, ...) for a AP1100, I decided to give a chance to the EQ8. I think it has a good quality/price ratio. Only time will tell me if I made a good choice...

Conclusion, it seems to have similar PE as the CGE Pro, with a similar price as the CGE Pro. But I think it carries more payload?

The EQ8 payload capacity is 50 kg or 110 lbs and you can use EQMOD! It was a game changer for me.

Stephan

#12 end

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Posted 24 October 2013 - 08:13 PM

If that is the typical PE that this mount has, it looks to be a good performer. Somewhat better than my CGE PRO and somewhat cheaper as well! It seems likely to me that a rebranded version of this mount will eventually replace the CGE PRO.

#13 pereloup

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Posted 25 October 2013 - 10:19 PM

One recommendation I would have is to shoot at a higher focal length, pempro recommends less than 2 arc/sec per pixel.


I used the EdgeHD with better resolution tonight. Pecprep calculates a PE of +/-2.8 arcsec. It's much better than the first try.

Posted Image

#14 orlyandico

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Posted 25 October 2013 - 10:24 PM

Looks good, so the basic mechanicals are sound. 6" p-p is a very good figure. I think if the rest of the mount holds up, the Losmandy Titan (and CGE Pro) would be in trouble..

#15 gavinm

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Posted 26 October 2013 - 12:16 AM

That isn't bad, is it.. nice work..

Hope mine arrives soon.






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